Showing papers in "Philosophical Magazine Part B in 2000"
TL;DR: In this paper, the authors present experimental results on the constant current stressing in hydrogenated amorphous silicon (a-Si:H) Cr−p+−V thin film devices.
Abstract: Experimental results on the constant current stressing in hydrogenated amorphous silicon (a-Si:H) Cr–p+–V thin film devices are presented. With increasing injection of charge via either increasing bias or time, the current-voltage characteristics of devices exhibit instability, as shown by a decrease in the reverse current. This is interpreted in terms of the creation of defects in the a-Si:H. The defect generation rate. as measured by the voltage shift ΔV at a constant reverse current in the J-V curve, is found to follow a square-root time dependent law. In addition, a decrease in device conductance after stressing is also observed, which is described by a mechanism of dopant equilibrium during and after stressing.
89 citations
TL;DR: Raman scattering, 119Sn Mossbauer spectroscopy and temperature-modulated differential scanning calorimetry experiments have been performed on (Ge0.99 Sn 0.01)x Se1−x glasses in the 0.36 range as mentioned in this paper.
Abstract: Raman scattering, 119Sn Mossbauer spectroscopy and temperature-modulated differential scanning calorimetry experiments have been performed on (Ge0.99 Sn0.01)x Se1−x glasses in the 0.30 < x < 0.36 range. Both Raman and Mossbauer spectroscopies show that Ge[sbnd]Ge signatures first appear near x = 0.31(1), and their concentration slowly increases with increasing x to acquire a value of 1.92(30)% at x = 1/3, corresponding to GeSe2 glass. Thereafter (1/3 < x < 0.36) the concentration of these bonds increases precipitously with increasing x. Glass transition temperatures T g(x) reflect the connectivity of the network and are found to increase with increasing x; however, the rate dTg/dx of T g increase slows down markedly at (i) x ≥ 0.31(1), and the rate actually reverses sign (ii) at x ≥ 0.34. Feature (i) coincides with nucleation and (ii) with precipitous growth of Ge[sbnd]Ge signatures. These T g trends show that the presence of Ge[sbnd]Ge signatures decreases the global connectivity of the glasses....
86 citations
TL;DR: In this paper, a self-consistent tight-binding formalism is presented to calculate the forces on individual atoms due to the flow of electrical current in atomic-scale conductors.
Abstract: We present a self-consistent tight-binding formalism to calculate the forces on individual atoms due to the flow of electrical current in atomic-scale conductors. Simultaneously with the forces, the method yields the local current density and the local potential in the presence of current flow, allowing a direct comparison between these auantities. The method is applicable to structures of arbitrary atomie geometry and can be used to model current-induced mechanical effects in realistic nanoscale junctions and wires. The formalism is implemented within a simple ls tight-binding model and is applied to two model structurest atomie chains and a nanoscale wire containing a vacancy.
71 citations
TL;DR: In this article, two multichannel systems based on a superconducting quantum interference device (SQUID) for biomagnetic measurements, installed at the University of Chieti, are presented.
Abstract: We present two multichannel systems based on a superconducting quantum interference device (SQUID) for biomagnetic measurements, installed at the University of Chieti. Both systems have been designed for clinical and routine use and have been developed owing to an international cooperation. The main issues in the instrument implementation were field sensitivity and spatial resolution, as well as flexibility and stability during operation. The first system is a planar system and is devised for magnetocardiographic measurements. This system is composed of 74 dc SQUID integrated magnetometers contained in a low-noise dewar: 55 sensors are measurement channels and 21 are placed far from the subject and are used as reference channels to create software gradiometers. The second system is a helmet system and consists of 165 de SQUID integrated magnetometers to perform magnetoencephalographic recordings; 153 channels are distributed over a surface covering the whole scalp and 12 channels are used as references. The field noise of the SQUID magnetometers is about 5 fT Hz -1/2 . Each system is placed in a magnetically shielded room for eddy current shielding and magnetic shielding. The magnetic field is recorded with sampling frequencies up to 10 kHz. The analogue-to-digital converted data are processed on line by means of an array of digital signal processors, allowing bandpass filtering, decimation and noise compensation.
69 citations
TL;DR: In this paper, the anomalous melting points of the light actinides can be understood in terms of the temperature dependences of their elastic properties, and they have extended the Lindemann rule to include temperature-induced elastic softening.
Abstract: In this paper, we apply the Lindemann melting rule to the analysis of Debye-Waller factor data obtained by neutron powder diffraction for several light actinide phases. The anomalous melting points of the light actinides can be understood in terms of the temperature dependences of their elastic properties. We have extended the Lindemann rule to include temperature-induced elastic softening.
60 citations
TL;DR: In this paper, the de Haasvan Alphen and Shubnikov-de Haas experiments were carried out on UX2 (X = Bi, Sb, As or P) and found quasi-two-dimensional Fermi surfaces in these compounds.
Abstract: We succeeded in growing high-quality single crystals of UX2 (X = Bi, Sb, As or P) by the self-flux and chemical transport methods and carried out de Haasvan Alphen and Shubnikov-de Haas experiments. We found quasi-two-dimensional Fermi surfaces in these U compounds. Fermi surfaces of UBi2 are found to consist of one spherical Fermi surface and two cylindrical Fermi surfaces. Each Fermi surface in UBi2 changes into two cylindrical surfaces in USb2 and UAs2. This change in the Fermi surfaces is well explained on the basis of a fiat magnetic Brillouin zone. The quasi-two-dimensional character of the Fermi surfaces is mainly due to the conduction electrons in the U piane, including the 5f electrons. The itinerant nature of 5f electrons is reflected in the large cyclotron masses. The magnetic breakthrough (breakdown) phenomenon is also discussed for USb2.
54 citations
TL;DR: In this paper, the formation of the silver nanoparticles leads to an increase of the optical absorption bends at the plasma wavelength in the visible range, where the spectral position of the transmittance minimum depends on the implantation conditions.
Abstract: Silver nanoparticles have been synthesized by ion implantation at 30 keV into polymethyl-methacrylate at doses from 3.1 × 1015 to 7.5 × 1016 ion cm−2 and a beam current 4 μA cm−2 at room temperature. Transmission electron microscopy was used to determine the structure of the silver-polymer systems obtained. It was observed that in the prepared samples, spherical metal particles with sizes smaller than 12 nm were fabricated. For characterization of the optical response of the composites, transmittance spectroscopy was employed. The formation of the silver nanoparticles leads to an increase of the optical absorption bends at the plasma wavelength in the visible range, where the spectral position of the transmittance minimum depends on the implantation conditions. It was observed that the intensity of the absorption is very weak in spite of the large quantity of silver particles existing in the polymer medium; the factors influencing the optical data are discussed.
50 citations
TL;DR: For an infinite three-dimensional transversely isotropic piezoelectric material, Green's functions (which give the fuli set of electromechanical fields due to a point electric charge and an arbitrarily oriented point force) were derived in a simple way, using methods of the potential theory as discussed by the authors.
Abstract: For an infinite three-dimensional transversely isotropic piezoelectric material, Green's functions (which give the fuli set of electromechanical fields due to a point electric charge and an arbitrarily oriented point force) are derived in elementary functions in a simple way, using methods of the potential theory. For a semi-infinite transversely isotropic piezoelectric material. Green's functions are also derived, but in a limited way: a point force and a point electric charge are assumed to be applied at the boundary of the half-space. The latter solutions constitute a generalization of Boussinesqs and Cerruti's problems of elasticity for piezoelectric materials. The strength of the piezoeffect (the difference from the purely elastic case) is estimated for the example of the piezoceramics PZT-6B.
46 citations
TL;DR: In this article, the Coulomb pseudopotential V(L) (pair energy as a function of pair angular momentum) in the lowest Landau level (LL) is defined that leads to short-range Laughlin-like correlations in many-body systems and to which the CF model can be applied.
Abstract: The mean-field composite fermion (CF) picture successfully predicts angular momenta of multiplets forming the lowest-energy band in fractional auantum Hall (FQH) systems. This success cannot be attributed to a cancellation between Coulomb and Chern-Simons interactions beyond the mean field, because these interactions have totally different energy scales. Rather, it results from the behaviour of the Coulomb pseudopotential V(L) (pair energy as a function of pair angular momentum) in the lowest Landau level (LL). The class of short-range repulsive pseudopotentials is defined that lead to short-range Laughlin-like correlations in many-body systems and to which the CF model can be applied. These Laughlin correlations are described quantitatively using the formalism of fractional parentage. The discussion is illustrated with an analysis of the energy spectra obtained in numerical diagonalization of up to 11 electrons in the lowest and excited LLs. The qualitative difference in the behaviour of V(L)is ...
34 citations
TL;DR: In this article, the Schrodinger operator on graphs is studied and the spectral statistics of a unitary operator which represents the quantum evolution of a quantum map on the graph are derived.
Abstract: We consider the Schrodinger operator on graphs and study the spectral statistics of a unitary operator which represents the quantum evolution, or a quantum map on the graph. This operator is the quantum analogue of the classical evolution operator of the corresponding classical dynamics on the same graph. We derive a trace formula, which expresses the spectral density of the quantum operator in terms of periodic orbits on the graph, and show that one can reduce the computation of the two-point spectral correlation function to a well defined combinatorial problem. We illustrate this approach by considering an ensemble of simple graphs. We prove by a direct computation that the two-point correlation function coincides with the circular unitary ensemble expression for 2 × 2 matrices. We derive the same result using the periodic orbit approach in its combinatorial guise. This involves the use of advanced combinatorial techniques which we explain.
32 citations
TL;DR: In this paper, an evaluation of transient photocurrent and modulated photocurrent (MPC) spectroscopies as a means of studying the density and capture properties of localized states in amorphous semiconductors is presented.
Abstract: An evaluation of transient photocurrent (TPC) and modulated photocurrent (MPC) spectroscopies as a means of studying the density and capture properties of localized states in amorphous semiconductors is presented. Freauency-domain analysis of TPC data via the discrete Fourier transform (TPC FT) permits a direct comparison with MPC data obtained using conventional lock-in techniaues to be made. Results obtained from undoped hydrogenated amorphous silicon over a wide range of temperatures and optical excitations are used to explore the limits of resolution and applicability, and to highlight the relative merits, of each approach. It is shown that TPC spectroscopy offers significant practical advantages over MPC spectroscopy from the viewpoint of signal-to-noise performance. Discrepancies between TPC FT and MPC data obtained from the same sample under equivalent conditions suggest that the Fourier transform pairing of these methods is not exact, even when the reauirements of low excitation are met. ...
TL;DR: In this paper, the bcc-fcc transition in Ni−Al, Al−Cu−Zn and Fe−Ni alloys is studied using semi-empirical model potentials.
Abstract: Martensitic transformations in nonmagnetic and magnetic transition-metal alloys have been studied by molecular-dynamics simulations using semi-empirical model potentials. In addition ab initio total energy calculations have been used to discuss the energy barrier between the different crystal structures and the minimal energy required for nucleation. The calculated mixing energies are a reliable tool to check the overall tendency for segregation of the alloys. Results of simulations for the bcc-fcc transition in Ni−Al, Al−Cu−Zn and Fe−Ni alloys are discussed.
TL;DR: In this paper, a supercell model and periodic auantum-chemical calculation scheme are used to study pure and Nb-doped CaTiO3 crystal, and geometry optimization is carried out in order to find the eauilibrium spatial structures of both cubic and orthorhombic phases, as well as to predict the most stable configurations of the Nb atom in these crystalline lattices.
Abstract: There exists experimental evidence that several properties of the CaTiO3 crystal, such as electrical conductivity and ferroelectricity, strongly depend on the Nb doping. In particular, if the concentration of Nb impurities is sufficiently high, a drastic increase in the electrical conductivity is observed. A supercell model and periodic auantum-chemical calculation scheme are used to study pure and Nb-doped crystals. The geometry optimization is carried out in order to find the eauilibrium spatial structures of both cubic and orthorhombic phases, as well as to predict the most stable configurations of the Nb atom in these crystalline lattices. The obtained relaxation energies of 3.83 eV for the cubic phase and 15.04eV for the orthorhombic phase are discussed, and their difference is explained. The composition of the electronic energy bands is analysed in comparison with the available experimental data. The increase in the electrical conductivity in the Nb-doped material for the orthorhombic phase...
TL;DR: In this article, the spectrum of the frustrated Heisenberg antiferromagnet was analyzed and the stability and structure of the spectrum including the two-particle singlet branch throughout the disordered phase, as well as in the vicinity of the Neel critical point.
Abstract: We overview some recent work and present new results on the ground-state properties and the spectrum of excitations of the two-dimensional frustrated Heisenberg antiferromagnet. Spontaneous dimer order is present in the quantum disordered phase of this model. We study the stability and analyse the structure of the spectrum, including the two-particle singlet excitation branch throughout the disordered phase, as well as in the vicinity of the Neel critical point. The variation in the dimer order parameter is also given, and it is argued that near the critical point it reflects the presence of the low-energy singlet bound state.
TL;DR: In this paper, the elastic moduli of the C15 Laves-phase materials TaV2, TaV 2H(D),x and ZrCr2 have been measured using the technique of resonant ultrasound spectroscopy.
Abstract: The elastic moduli of the C15 Laves-phase materials TaV2, TaV2H(D),x and ZrCr2 have been measured using the technique of resonant ultrasound spectroscopy. The temperature dependences of the shear modulus and Young's modulus of TaV2 were found to be anomalous; the moduli increase with increasing temperature over the entire temperature range 4-345 K. In contrast, the shear modulus and Young's modulus of TaV2H0.34, TaV2H0.53 and TaV2D0 17 all decrease with increasing temperature. The bulk moduli of these materials are only weakly temperature dependent. The elastic moduli of the C15 Laves-phase compound ZrCr2 exhibit a normal temperature dependence over the range 20-300 K. The unusual elastic behaviour of these materials is accounted for by a model involving electronic contributions to the elastic constant c44. The symmetry of the C15 structure results in doubly degenerate electronic energy levels at the X point of the Brillouin zone. The strain dependence of these levels affects the elastic constant...
TL;DR: In this article, the influence of inelastic tunnelling processes, metal at the interface and material properties on the junction magnetoresistance (JMR) of spin-polarized ferromagnetic (FM/I/FM) metals is discussed.
Abstract: The pioneering studies of spin-polarized tunnelling by Meservey and Tedrow in the early 1970s showed that the conduction electrons in ferromagnetic (FM) metals are spin polarized and that the spin is conserved in the tunnelling process. Only recently (1995) improved material fabrication techniques have permitted realization of the Julliere quantitative model, showing that tunnelling in ferromagnet/insulator/ferromagnet (FM/I/FM) junctions should lead to a large junction magnetoresistance (JMR); JMR values greater than 30% have been achieved at room temperature. This recent success has led to several fundamental questions regarding the phenomenon of spin tunnelling and also the development of JMR devices. In this paper, experimental results, such as the dependence on bias, temperature and barrier characteristics of FM/I/FM tunnelling are reviewed briefly. The influence of inelastic tunnelling processes, metal at the interface and material properties on the JMR is discussed. The future direction from both the physics and the applications viewpoints, is also covered.
TL;DR: In this article, the nucleation of grains by subgrain growth has been investigated using a two-dimensional vertex model, where the initial geometry has an on average flat grain boundary, separating two populations of subgrains.
Abstract: The nucleation of grains by subgrain growth has been investigated using a two-dimensional vertex model. The initial geometry has an on average flat grain boundary, separating two populations of subgrains. The phenomenon has been studied using (i) a constant ratio between the subgrain and the grain boundary mobility or energy and (ii) simple relations for the misorientation dependencies of these two quantities. Bulging of grain boundaries owing to subgrain growth at topologically favoured sites has been observed. A subgrain size gradient at the grain boundary reduces the bulging frequency and leads to a general drift of the grain boundary.
TL;DR: In this paper, the heat capacity and thermal expansion of cubic (fcc-disordered) and tetragonal (DO22-ordered) Pd3V were measured from 40 K to 315 K.
Abstract: Differences in the heat capacity and thermal expansion of cubic (fcc-disordered) and tetragonal (DO22-ordered) Pd3V were measured from 40 K to 315 K. Below 100 K the heat capacity difference was consistent with harmonie vibrations. At higher temperatures, however, the data show significant anharmonic effeets. Measurements of elastic constants. densities and thermal expansion showed that the anharmonic volume expansion contribution (CP - CV ) could account for only about one-third of this anharmonic heat capacity difference. The remainder may originate with elastic and plastic deformation of the polycrystalline microstructure. Strain energy from anisotropic thermal contractions of grains in the tetragonal ordered phase contributes to the heat capacity, but some of this strain energy is eliminated by plastic deformation. The vibrational entropy difference of disordered and ordered Pd3V was estimated to be Sdis - Sord = (+0.035 ± 0.001)K B/atom at 300 K. with 70% of this coming from anharmonic effeets.
TL;DR: In this article, BaTiO3/p-Si interfaces were examined by admittance spectroscopy, currentvoltage and transient current measurements, and X-ray diffraction (XRD) characterization.
Abstract: Thin films of BaTiO3 were deposited on p-Si substrates by rf magnetron sputtering in order to investigate their suitability for use in ac thin film electroluminescent (ACTFEL) devices and dynamic RAM (DRAM) applications. Post-growth annealing at 700°C and the subseauent deposition of Al contacts resulted in the creation of Al/BaTiO3/p-Si metal-insulator-semiconductor devices. The electronic and structural properties of the films were examined by admittance spectroscopy, current-voltage and transient current measurements, and X-ray diffraction (XRD) characterization. Analysis of the XRD spectra showed the polycrystalline nature of the films but also the presence of an amorphous phase. The electrical measurements revealed a high dielectric constant, around 60, a charge storage capacity exceeding 3 μC cm−2 and a total charge trapped inside the oxide of around 50 nC cm−2 while the density of traps at the BaTiO3/p-Si interface was found to be as high as 1 × 1012 cm−2 eV−1. These results indicate that ...
TL;DR: In this article, the physical mechanisms of hydrogen-induced silicon surface cleavage were investigated using the combination of cross section transmission electron microscopy (XTEM) and Rutherford back-scattering spectrometry (RBS) channelling analysis.
Abstract: The physical mechanisms of hydrogen-induced silicon surface cleavage were investigated using the combination of cross section transmission electron microscopy (XTEM) and Rutherford back-scattering spectrometry (RBS) channelling analysis. A 〈100〉-oriented silicon wafer was implanted with 175 keV protons to a dose of 5 × 1016 cm−2. The implanted wafer was bonded to a SiO2-capped 〈100〉-oriented silicon wafer and then heated to an elevated temperature of 600°C to produce exfoliation. The damage region of the implanted silicon was examined by XTEM, which revealed the presence of hydrogen-filled platelets. The depth distribution of the implantation damage was also monitored by RBS in the channelling condition in the as-implanted state as well as after the cleavage of the silicon wafer. A comparison of the RBS and XTEM indicates that the nucleation of hydrogen-filled microcavities and the cleavage of the silicon wafer take place above the hydrogen concentration peak near the implantation damage peak, re...
TL;DR: In this article, the electronic structure and bonding in the (Na15/32Bi½)TiO3 (NBT) crystal and its solid solution with BaTiO 3 (BT) are studied by first-principles local density calculations.
Abstract: The electronic structure and bonding in the (Na15/32Bi½)TiO3 (NBT) crystal and its solid solution with BaTiO3 (BT) are studied by first-principles local density calculations. For the solid solution. an ordered superstructure (Na15/32Bi15/32Ba1/16)TiO3 with 320 atoms in a large celi is proposed. The results show that both NBT and NBT-BT are semiconductors with a band gap of about 1 eV. NBT is shown to be a harder crystal than PbTiO3 and PbZrO3 by having a larger calculated bulk modulus. This can be attributed partly to the increased covalent character of bonding in NBT and NBT-BT crystals. The calculated O K edges for a number of related crystals are presented and compared. It is suggested that electron energy loss near-edge structure measurements can be an effective tool to characterize the samples for different piezoelectric materials.
TL;DR: In this paper, the influence of magnetic fields on the athermal and isothermal martensitic transformations of Fe-Ni and Cu-Al-Ni alloys has been examined.
Abstract: The influence of hydrostatic pressure and magnetic fields on the athermal and the isothermal martensitic transformations in Fe-29.9at.% Ni, Fe-31.7at.% Ni, Fe-32.3 at.% Ni, Cu-29.1 at.% Al-3.6 at.% Ni and Fe-24.0 at.% Ni-4.0 at.% Mn alloys have been examined in order to clarify the difference between the athermal and isothermal transformation processes. The following results were obtained. Firstly, a martensitic transformation occurs after some incubation time during isothermal holding at a temperature higher than the transformation start temperature Ms in zero external field and no hydrostatic pressure for Fe-Ni and Cu-Al-Ni alloys which originally exhibit athermal martensitic transformations. Secondly, athermal martensitic transformations in Fe-Ni alloys change to isothermal transformations under hydrostatic pressure. Thirdly, in the isothermal martensitic transformation in an Fe-Ni-Mn alloy, a static magnetic field lowers the nose temperature and increases the incubation time reauired for the ...
TL;DR: In this article, a new technique for analysing diffuse scattering based on Rietveld analysis was described, and applied to data for δ-phase Pu0.98Ga0.02 alloy.
Abstract: In an earlier paper (Lawson et al., 2000, Phil. Mug. B, 80, 53) we described the measurement and interpretation of Debye–Waller factors in a δ-phase Pu0.98Ga0.02 alloy. We concluded that the measurements could be described using a Debye model with a strongly temperature-dependent Debye-Waller temperature. In those experiments, we observed significant diffuse scattering in the neutron powder diffraction patterns. In this paper we describe a new technique for analysing diffuse scattering based on Rietveld analysis, and apply the technique to data for δ-phase Pu0.98Ga0.02 and for Pb. The results from the correlations among lattice vibrations show that the diffuse scattering is Warren–Borie scattering and that the diffuse scattering is in basic agreement with that expected from the Debye model except that the scattering from the nearest-neighbour correlations in Pu0.98Ga0.02 is anomalous at high temperatures. We also discuss the observation of significant anisotropic broadening of the diffraction pea...
TL;DR: In this article, two sets of activation barriers were used in the simulation and the influence of the probabilities of different hopping events on the growth has been studied, based on simple bond-counting energetics.
Abstract: Time-resolved in situ-applied scanning tunnelling microscopy (STM) has been used to study the homoepitaxial growth of Fe on Fe(ll0). Sequences of STM images taken during growth directly show the atomistics of the growth processes on the surface. These data are statistically analysed and compared with kinetic Monte Carlo simulations which include the correct symmetry of the bcc (110) surface. Two sets of activation barriers were used in the simulation. Applying simple bond-counting energetics the influence of the probabilities of different hopping events on the growth has been studied. Material-specific barriers calculated using a Finnis-Sinclair potential reproduce most of the real growth behaviour. A strongly anisotropic growth is found with islands elongated in [001] which is kinetically stabilized by a hindered diffusion at step edges along [001]. At room temperature, the presence of a step edge barrier prevents the interlayer mass transport nearly completely and leads to kinetic roughening an...
TL;DR: In this paper, the role of different metal contacts on the performances of one-dimensional thin-film position-sensitive detectors produced by plasmaenhanced chemical vapour deposition, to be used in optical rulers for alignment applications was determined.
Abstract: The aim of this work is to determine the role of different metal contacts on the performances of one-dimensional thin-film position-sensitive detectors produced by plasma-enhanced chemical vapour deposition, to be used in optical rulers for alignment applications. The device consists on an indium tin oxide/p-i-n structure where the metal contacts used were based on Al, Al + Cu and Ag. The results achieved show that the contact mainly influences the final sensor range by limiting the magnitude of the analogue signals recorded. In spite of soldering problems the Al contact was the contact that lead to better discrimination of the sensor, with a nonlinearity of ± 0.8% and a fall-off parameter of 3.2 × 103 cm−1. The Al + Cu contact also exhibits good performances (nonlinearity, of ±1.1%; fall-off parameter, 1.4 × 10−2cm−1) and should be chosen since it is much easier to solder but requires protection against oxidation. The integration of these sensors on the optical ruler lead to the production of a ...
TL;DR: In this article, it was shown that there are two routes of electrical transport in luminescent porous silicon, one between silicon crystallites and the other through a disordered silicon compound tissue that wraps the crystallites.
Abstract: It is shown that there are two routes of electrical transport in luminescent porous silicon. The first is between silicon crystallites and the other is through a disordered silicon compound tissue that wraps the crystallites. The conduction mechanism in the first route is similar to that encountered in granular metals, that is tunnelling dominated by the crystallites' charging energy. The conduction mechanism in the second route is similar to that encountered in hydrogenated amorphous silicon, that is extended-states transport in a disordered semi-conductor. The implication of these findings on the prospects of efficient electroluminescence in porous silicon are discussed.
TL;DR: In this paper, the structure of hydrogenated microcrystralline silicon (mc-Si: H) films deposited by hot-wire chemical vapour deposition was investigated by means of X-ray diffraction (XRD) and infrared (IR) spectroscopy.
Abstract: The structure of hydrogenated microcrystralline silicon (mc-Si: H) films deposited by hot-wire chemical vapour deposition was investigated by means of X-ray diffraction (XRD) and infrared (IR) spectroscopy. Roughly random orientation of crystallites grained preferentially by (111) planes was established by XRD. The behaviour of IR absorption lines were analysed with respect to the variation in mean grain sizes and high-temperature treatments. As was established, the characteristic features of IR absorption in mc-Si: H come from the bonding of hydrogen on grain boundaries in the form of monohydrides and polyhydride groups and the splitting of absorption bands. The latter was interpreted in terms of absorption of optically anisotropic SiH monolayers covering the internal surfaces in mc-Si: H.
TL;DR: Fe and its alloys in the fcc structure reveal a variety of phases which, depending on the composition and temperature, show Invar and anti-Invar effects as well as martensitic transformations and s...
Abstract: Fe and its alloys in the fcc structure reveal a variety of phases which, depending on the composition and temperature, show Invar and anti-Invar effects as well as martensitic transformations and s...
TL;DR: In this paper, the photoluminescence properties of thin SiO2/Si layers obtained by low-pressure chemical vapour phase deposition and thermal oxidation processes were investigated.
Abstract: The recent progress accomplished in our research group is here presented. Firstly porous Si (PS) microcavities were formed on p-type-doped (6-9ωcm) substrates with very narrow bandwidth (6 nm) and a good ratio of the peak to background emission, reaching at the same time a high emission quantum efficiency. Secondly light-emitting diodes (LEDs) based on n-type-doped Si/PS heterojunctions were studied. The improvement in the proposed LED structure with respect to the usual metal/PS LED is demonstrated. Anodic oxidation experiments show further improvements in the LED efficiency. Thirdly, SiO2/ Si/SiO2 quantum wells with room-temperature efficient light emission in the visible range were investigated. We report here the preparation and photoluminescence properties of thin SiO2/Si layers obtained by low-pressure chemical vapour-phase deposition and thermal oxidation processes. The growth technique is fully compatible with standard very-large-scale integration complementary metal-oxide-semiconductor t...
TL;DR: An analytical model for the electric field associated with a periodic array of alternating p-and n-doped stripes lying in a half-plane, tilted with respect to the specimen edges and thus better representing the actual experimental set-up is presented in this article.
Abstract: An analytical model for the electric field associated with a periodic array of alternating p- and n-doped stripes lying in a half-plane, tilted with respect to the specimen edges and thus better representing the actual experimental set-up is presented. With respect to a previous treatment, relative to the case of stripes perpendicular to the edge, a more physical derivation is outlined, and the calculated phase shift is used to interpret the main features of holography and Lorentz microscopy images, allowing a quantitative assessment of the influence of the specimen edge on them.